Transient High-Temperature Superconductivity in Palladium Hydride

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Abstract

Superconductivity in the palladium-hydrogen system has been studied experimentally by measuring the electrical resistivity. Loading a palladium sample to a stoichiometric ratio close to unity resulted in high-temperature superconductivity at ≈ 55 K for PdHx and ≈ 60 K for PdDx. To observe the superconductivity it was necessary to cool the sample quickly from 300 C and measure the resistivity while heating quickly.
For this project an important driver was a series of publications reporting the occurrence of superconductivity near room temperature with hydrogen-to-palladium ratio reaching 1. These results are still considered as controversial because they have not been reproduced. One of the other important driving factors was that PdHx formed at about 300 C exhibits different behaviour compared to the hydride formed by passage through the two-phase region at room temperature. This system does not form dislocations if the hydrogen absorption takes place above the thermodynamic critical point, which lies just below 300 C.
In the 1970s, a superconducting transition temperature, Tc, of about 9–10 K was reported for pallidum hydride and 11–12 K for palladium deuteride. The new experiments performed in this project revealed that Tc has increased by a factor of about five by preparing the sample at high temperature.